I wonder what the difference in ability is between a development rider and a racer ? Suzuki has a relatively small budget compared to the other Factory teams and perhaps they want to target podiums (=success) rather than have once rider with a racer mentality and one development rider who can also race, but perhaps lacks that last 10% of the mentality of a true racer and therefore potentially reduces their chances of a podium?

There are very few racers who can truly develop a bike at the same time. Sure, they can give feedback but they don't have the time or perhaps the skill to do endless laps of a circuit and then give the feedback thats necessary for an engineer to change into torsion stiffness of a swing arm or chassis flex.